I had an already existing project and i imported the AppCloudServices module, i followed this documentation https://world.mendix.com/display/howto50/2a.+Introducing+AppCloud+Services+In+Your+Existing+App but i am getting this error: Couldn't deploy to your sandbox. Please try again, if you encounter this error again, please contact support
Douglass, there have been some deployment issues before. End of this month Modeler 5.6 will be released.
That release contains some fixes for cloud deployment issues and that version should solve your problems as well.